FR2828464A1 - Hydraulic circuit for braking, comprises sensor which detects brake pedal movement and releases an injection of hydraulic fluid sufficient to refeed the braking circuits and eliminate delay - Google Patents

Abstract

An hydraulic braking circuit (1) is connected to a braking unit (4) and is operated by a brake pedal (6), a servomotor (9) and a master cylinder (2) with reservoir (3). A means (7) of injecting sufficient hydraulic fluid to eliminate delay includes an electrovalve (17), a hydraulic reservoir (16) under spring pressure and a compartmented drawer type electrovalve (15). The means are activated when a sensor (5) detects brake pedal movement An Independent claim is also included for: Utilisation of hydraulic braking circuit which includes stage of injection of hydraulic fluid after detection of braking pedal movement

Description

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Hydraulic brake system and its use
The present invention relates to a hydraulic braking circuit associated with a device making it possible to reduce the dead stroke of a vehicle during braking, in particular when a driver's foot is pressed on a brake pedal. It also relates to its use. The invention thus aims to improve the very beginning of the braking phase of a vehicle by making it more efficient and less tiring for the driver's foot to be pressed on the vehicle's brake pedal.

 When a driver presses with his foot on a brake pedal of a vehicle, a control rod connected to this brake pedal moves at least one piston of a master cylinder of a hydraulic braking circuit.

The piston compresses a volume of hydraulic fluid contained in at least one chamber of the master cylinder. This compression results in hydraulic fluid pressure at the outlet of the master cylinder.

 The hydraulic pressure causes the hydraulic fluid to move in the various conduits of the hydraulic braking circuit.

This hydraulic pressure makes it possible to brake at least one wheel of the vehicle. For example, this hydraulic fluid, by its pressure, can compress brake pads against brake discs fixed to a hub of at least one wheel of the vehicle.

 At the end of braking, part of the hydraulic fluid present in the conduits of the hydraulic braking circuit returns to the master cylinder. This return of the hydraulic fluid to the master cylinder takes place by releasing the pressure in the master cylinder, and due to the various restoring forces exerted on the elements of the circuit. For the rest, the liquid stagnates in the conduits of the hydraulic braking circuit.

 Thus, during the very first stages of the following braking, before acting directly on the actual braking mechanism, the displacement of the hydraulic fluid leaving the master cylinder must catch up with the entire dead stroke, in particular the displacement of the hydraulic fluid must serve to tackle the brake pads against the brake discs. The hydraulic fluid must also make up for the play in the hydraulic circuit resulting from the openings or closings of certain non-return valves of this hydraulic circuit. The period during which the hydraulic fluid must make up for the clearances of the

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 circuit corresponds to the duration of catching up the dead travel of the brake pedal. The dead travel of a brake pedal is, in practice, the distance that a brake pedal must travel before its action causes the vehicle to brake. The period of the dead race delays the braking in a manner deemed unacceptable in some cases.

 Thus, conventionally, during the very first stages of braking, the flow at the outlet of the master cylinder comprises the actual hydraulic flow serving to brake the vehicle and, beforehand, a hydraulic loss flow serving, inter alia, to compensate for the clearances of the circuit. hydraulic braking. This hydraulic loss flow results, in a way, from an absorption of the hydraulic braking circuit.

 It is in the driver's interest, for greater safety, that the flow rate at the outlet of the master cylinder be as efficient as possible. The efficiency of such a flow would reside in a flow used only for braking the vehicle. For this, one could decrease the absorption of the hydraulic circuit and decrease the reaction time of the hydraulic circuit. However, this work would be complex and would not solve the problem of wear of the parts of the hydraulic circuit over time and their use. The realization of such a solution would be expensive anyway.

 Currently, to reduce the absorption during the braking phase, a mechanical device is used which is used between the booster and the master cylinder. However, such a device does not make it possible to reduce all of the absorption.

 To reduce absorption in the hydraulic circuit, the invention provides for the installation of a hydraulic device located at the outlet of the master cylinder. This hydraulic device makes it possible to make up for these clearances in the hydraulic braking circuit. This hydraulic device is preferably located downstream and close to the master cylinder and operates at the very start of the braking phase, during the very first millimeters of travel. By this hydraulic device, the hydraulic flow at the outlet of the master cylinder can be used more to brake the vehicle.

 With this hydraulic device, the invention consists in filling the conduits of the hydraulic braking circuit with hydraulic fluid, at the very beginning of the braking phase, so as to reduce the absorption phase. This reduction of the absorption phase is carried out in such a way that a

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 slight pressure is obtained at the outlet of the master cylinder in the hydraulic circuit, before the flow leaving the master cylinder causes the vehicle to brake.

 According to the invention, the liquid intended to force-feed the conduits of the hydraulic braking circuit comes from a source other than that coming from the hydraulic fluid reservoir, which is usually located above the master cylinder. This liquid comes from a chamber which has the particularity of containing hydraulic liquid under a certain pressure. This pressurizing of the liquid makes it possible to inject the liquid into the circuit so that the circuit is placed under slight pressure before the actual braking of the vehicle. The chamber must contain a volume of hydraulic fluid under pressure such that this volume makes it possible to make up for the clearances in the circuit.

 According to the invention, at the very beginning of the braking phase, the displacement of the brake pedal is detected by a displacement sensor of the brake pedal. This sensor acts indirectly on the chamber and causes it to open. Three cases can then arise.

 In the first case, the opening of the chamber is followed by the injection of the liquid into the hydraulic braking circuit, in order to force-feed the circuit at the very start of the braking phase. The chamber is again filled during a subsequent brake release phase, in particular by temporarily disconnecting the master cylinder from the hydraulic braking circuit while the chamber is filling.

 In the second case, the injection is carried out as in the first case.

On the other hand, the filling of the chamber occurs during subsequent braking. Sensors installed on the brake pedal can manage this filling. The implementation is then simpler and less costly. However, this results in a temporary decrease in the pressure available, during braking, at the place where the brakes are located.

 In the third case, the opening of the chamber following the movement of the brake pedal is not followed by its immediate filling. The hydraulic fluid is filled in the chamber when the vehicle is stopped and / or during the advance. This filling is carried out by bypassing the master cylinder in the hydraulic braking circuit.

 The invention therefore relates to a hydraulic braking circuit of a

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 vehicle comprising a brake pedal displacement sensor characterized in that it comprises means for triggering an injection, into the circuit, of a volume of hydraulic liquid corresponding to a quantity of liquid necessary to force-feed circuit conduits .

 The invention also relates to the use of a hydraulic braking circuit of a vehicle comprising a step in which - one presses on a brake pedal, characterized in that it comprises a step in which - one puts in service of the means of boosting the hydraulic circuit during a start of braking.

 The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These are presented for information only and in no way limit the invention. The figures show: - Figure 1: a schematic representation of a hydraulic braking circuit provided, according to the invention, with a device creating, before braking, a slight overpressure in the hydraulic circuit; - Figures 2a to 2f: graphical representations of the entanglement in time of the events leading to the boosting of the hydraulic braking circuit, at the very beginning of the braking phase of the vehicle, following the starting of the device according to the invention .

 Figure 1 shows a hydraulic braking circuit 1 according to the invention. The circuit 1 comprises a master cylinder 2, a reservoir 3 of hydraulic fluid, a braking device 4, and according to the invention a sensor 5 for measuring the displacement of a brake pedal 6. The sensor 5 is connected to a device 7 making it possible to create a slight pressure in the hydraulic braking circuit 1. The sensor 5 and the device 7 are an example of the means making it possible to trigger an injection in the circuit 1.

 The brake pedal 6 is connected to a control rod 8. This control rod 8 is itself connected, preferably, to an assistance member, such as, for example, a servomotor 9. The servomotor 9 is itself mechanically connected to the master cylinder 2. This master cylinder 2 is supplied with hydraulic fluid 10 by the reservoir 3 of hydraulic fluid situated above the master cylinder 2. From the master cylinder 2, two conduits 11 and 12 come out to supply the device 4 braking. A bypass 13 is taken from the conduit 11. The braking device 4 comprises a set of

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 conduits represented very schematically by the dashed frame.

 This set of conduits leads to at least one wheel 14 of the vehicle.

 According to the invention, the hydraulic braking circuit 1 comprises the device 7 making it possible to create a slight pressure in the hydraulic braking circuit 1, before braking the vehicle. This device 7 is here located downstream of the master cylinder 2 and is connected to the conduit 11 by the bypass 13. In one example, this device 7 can be located as close as possible to the master cylinder 2, so as to force-feed as much possible ducts of circuit 1 from the master cylinder 2. In this way, the circuit can be force-fed as soon as it leaves the master cylinder 2 and the flow leaving the master cylinder 2 when braking the vehicle, can be used fully for braking the skids on the disk of at least one wheel 14 of the vehicle.

 The device 7 comprises, in the example, a compartmented drawer forming a solenoid valve 15, a chamber 16 containing hydraulic fluid 10 under pressure, and preferably a valve 17 at the outlet of the master cylinder 2, downstream of the bypass outlet 13 on the duct 11. The valve 17 can be, for example, a non-return valve.

 The solenoid valve 15 is a three-way valve. It has several compartments. In one example, the solenoid valve 15 comprises a drawer with two compartments 18 and 19 separated by a partition 20. The compartment 18 comprises a closed valve 21 and an orifice 22. The orifice 22 is provided to come opposite the bypass 13 The compartment 18 allows the passage of the hydraulic liquid 10 leaving the master cylinder 2. The compartment 18 comprises, for this purpose, a second orifice 23 connected to the braking device 4 by another conduit 24. The second compartment 19 comprises a second valve 25 closed and two ports 26.1 and 26.2. The two orifices 26.1 and 26.2 open into the compartment 19, allowing the solenoid valve 15, when it is advanced (dotted position), to form a passage between the chamber 16 containing hydraulic fluid and opening out through a conduit 27 and the braking device 4 via conduit 24.

 Chamber 16 is a container containing hydraulic fluid 10 under pressure. This liquid 10 is put under pressure by means of an artificial piston made by suspending a plate 28 from a spring 29. The spring 29 is in reaction, moreover, against an internal wall of the

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 chamber 16. The spring 29 can be in two different situations. This spring 29 can be extended and can be used to expel the liquid. In this situation, the spring 29 helps the liquid to leave the chamber 16 by exerting a pressure via the plate 28. The chamber 16 is then in a situation where it empties. The spring 29 can also be compressed by pressing on the plate 28 of the liquid 10 contained in this chamber 16. The chamber 16 is then in a situation where it is filled. A vacuum sensor 31 is connected to the chamber 16 by a conduit 32. It makes it possible to measure the pressure in the chamber 16 and to establish in correspondence the conditions for controlling the solenoid valve 15 and, preferably, also of the valve. 17.

 To allow filling of the chamber 16 during braking, at rest or during the running of the vehicle, the valve 17 is installed on the outlet duct 11 of the master cylinder 2. This valve 17 can be a non-return valve preventing the liquid from returning to the master cylinder 2. This valve 17 can be controlled as a function of a signal 33 or a signal 34 supplied respectively by the sensor 5 for displacement of the brake pedal, or by the sensor 31 for depression. These signals 33 and 34 are processed by a control member not shown (but of conventional invoice) and are transformed into orders 33.1 and 34.1 respectively addressed to the solenoid valve 15 and to the valve 17 to close the conduit 11.

Thus, the hydraulic fluid 10 can go towards the chamber 16 of the device 7 in order to fill the chamber 16 there.

 The operation of the device 7 associated with the sensor 5 for movement of the brake pedal 6 is described in FIGS. 2a to 2f. These figures respectively represent the braking of the vehicle, the opening of the chamber 16, the value of the pressure prevailing inside the chamber 16, the signal 34 delivered by the vacuum sensor 31, the signal 33 delivered by the sensor 5 movement of the brake pedal, and alternatively a temporary disconnection of the master cylinder. We are first interested in the case where the chamber is empty to force-feed the circuit, prior to the actual braking of the vehicle, and where the chamber fills with brake release.

 FIG. 2a shows, as a function of time (like all the others), the evolution of the position of the pedal 6 at the time of braking. During the very first millimeters of travel of the pedal 6, item 36, the pressure Pmax (FIG. 2c) prevailing inside the chamber 16 is at its maximum.

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 The brake pedal displacement sensor 5, FIG. 2e, indicates by a signal 33 converted into an order 33.1 to have to switch the solenoid valve 15 to open the chamber 16, FIG. 2b. The solenoid valve 15 then moves to connect the chamber 16 to the braking device 4 via the compartment 19.

 The solenoid valve 15 has moved to disengage the valve 21 from the conduit 27 so that the conduit 27, initially opening into the compartment 18 is now found facing the compartment 19. By this compartment 19, the conduit 27 is directly connected to the conduit 24. Through this conduit 24, the liquid contained in the chamber 16 can be injected and force-feed the hydraulic braking circuit 4. The conduit 13 connected to the master cylinder 2 is closed by the valve 25. This closure of the conduit 13 thus makes it possible to disconnect the master cylinder 2 from the device 7.

 As the chamber 16 empties, the pressure prevailing inside the chamber 16 decreases, FIG. 2c. It decreases to a pressure level Pmin corresponding to a volume of liquid necessary to eliminate the clearances in the hydraulic braking circuit 1. The pressure Pmin is at the same time that which prevails in circuit 1 under the effect of the braking imposed by the pedal 6. At this time, the vacuum sensor 31, FIG. 2d, indicates to the solenoid valve 15, by a signal 34 converted into an order 34.1 to have to close the chamber 16 figure 2b. The solenoid valve 15 then moves in such a way that the valve 21 comes to be placed at the place where the duct 27 is located. The liquid coming from the master cylinder 2 can then flow through the compartment 18 as far as the device 4 braking.

 The installation of this mechanism is such that the flow leaving the master cylinder 2 is thus assisted by the booster of the circuit 1. During the entire following duration 37 of braking, FIG. 2c, the vacuum sensor 31 of the chamber 16 detects the Pmin pressure in chamber 16.

 In order for the device 7 to operate under the next braking, the chamber 16 must be filled again. For this, the invention is implemented in such a way that it can take advantage of the consequences of braking during brake release. One of the consequences of braking is, among other things, the return to the master cylinder 2 of the hydraulic fluid during brake release by releasing the pressure in the master cylinder 2.

 The invention provides in this case for blocking the return of the liquid to the

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 master cylinder 2 for the benefit of filling the chamber 16 by the conduit 24. The return of this liquid can be blocked by the action of the valve 17 operating as a valve. Or else the valve 17 can be controlled, at the same time as the solenoid valve 15, by an order 33.2 resulting from the evolution of the signal 33, see FIGS. 2b, 2e and 2f, or by an order resulting from the measurement of the vacuum (signal 34). As the chamber 16 fills with liquid, the pressure inside the chamber 16 increases, FIG. 2c. When the chamber 16 is filled with at least a volume of liquid necessary to make up for the clearances of the circuit 1 and corresponding to the pressure Pmax, the vacuum sensor 31 indicates by a signal 34 converted into an order 34.2 to the solenoid valve 15 to be move in order to close the conduit 27 of the chamber 16, FIG. 2b, and the valve 17 to become on again.

 The starting of the device 7, in the case where the chamber 16 fills during the end of the braking of the vehicle, is also described in FIGS. 2a to 2f. During the braking of a vehicle, the driver presses harder and harder on the brake pedal 6 in order to achieve increasingly stronger braking of the vehicle (straight line dotted in continuity with the straight line in solid line, FIG. 2a ). During this stronger support, the chamber 16 is refilled. This filling can be triggered by a movement of the brake pedal 6 measured by the sensor 5 of movement of the brake pedal 6. This sensor 5 sends a signal 33 converted into an order 33.2, as for brake release, but for stronger braking in this case, to put the chamber 16 in communication with the braking device 4, but not to close the valve 17 in that case. It follows the same events as for the first case described above where the filling of the chamber would be carried out during the brake release.

 In the third case, where the filling of the chamber 16 can be carried out independently of the braking, during the stopping or during the running of the vehicle, the device 7 can be provided with a complementary hydraulic pump 38, FIG. 1. The pump 38 is connected in derivation of the master cylinder 2 between the reservoir 3, by a conduit 39, and the chamber 16, by a conduit 40. Thus, the pump 38 can be started by a signal 34 coming from the sensor 31 for measuring pressure in chamber 16 converted to an order 34.3. Hydraulic pump 38 draws liquid

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 hydraulic directly in the hydraulic tank 3 through the conduit 39. Then, the pump 38 fills the chamber 16 through the conduit 40 during the stopping or during the running of the vehicle. In the latter case, the filling of the chamber 16 does not cause any modification of the braking circuit.

Claims (9)

1-Hydraulic circuit (1) for braking a vehicle comprising a sensor (5) for displacement of a brake pedal (6) characterized in that it comprises means for triggering an injection, into the circuit, of a volume of hydraulic liquid corresponding to a quantity of liquid necessary to force-feed circuit conduits.  2-circuit (1) according to claim 1, characterized in that it comprises a master cylinder and in that the injection means (7) are located downstream of the master cylinder (2) relative to a reservoir (3 ), as close as possible to a master cylinder (2).  3-circuit (1) according to one of claims 1 or 2, characterized in that it comprises - a hydraulic fluid reservoir, a master cylinder, and brake lines (4), and in that the means d injection (7) comprise - a chamber (16) serving as an additional reservoir for hydraulic fluid, and containing a volume of hydraulic fluid corresponding to a quantity of liquid necessary to force-feed the conduits of the circuit, - a solenoid valve (15) connected to the chamber, to the master cylinder (2) and to the braking conduits, preferably in the form of a compartmentalized drawer, - a control device for regulating, over time, the opening and / or closing of the solenoid valve, and preferably - a valve (17) present at the outlet of a master cylinder (2).  4-circuit (1) according to claim 3, characterized in that the chamber (16) comprises a vacuum sensor (31).  5-circuit (1) according to one of claims 3 to 4, characterized in that the solenoid valve (15) has - two orifices (26.1 and 26.2) allowing the passage of hydraulic fluid (10) between the chamber (16) and the braking device (4), and - two orifices (22 and 23) allowing the passage of hydraulic fluid (10) between the master cylinder (2) and the braking device (4).  6-Use of a hydraulic braking circuit (1) of a vehicle comprising a step in which <Desc / Clms Page number 11>  - Pressing on a brake pedal (6), characterized in that it includes a step in which - means (7) are used to force-feed the hydraulic circuit (1) during the start of braking.  7 - Use according to claim 6, characterized in that - filling the feeding means during brake release of the vehicle.  8-Use according to one of claims 6 to 7, characterized in that - filling the filling means during braking of the vehicle.  9 - Use according to one of claims 6 to 8, characterized in that - filling the filling means during a stop or a movement of the vehicle.